Field of the Invention
The present invention relates, in general, to presses and, specifically, to hydraulic presses used in stamping or shearing operations and, more specifically, to control systems for hydraulic presses.
Workpieces are commonly punched or stamped from sheet metal in fluid operated or hydraulic presses. Such presses include a frame having a bed with a lower die mounted thereon. A fluid operated cylinder, such as a hydraulic cylinder, includes a movable piston mounted on the upper portion of the frame which drives a ram or punch having an upper die mounted thereon into a metal sheet disposed between the dies to punch or shear a workpiece from the metal sheet.
As the punch or upper die engages and moves through the metal sheet, forces on the order of several tons are introduced into the dies and the surrounding frame of the press which progressively increase to a maximum force load at the point of breakthrough of the upper die through the metal sheet. The forces are restrained during the shearing or stamping operation and are stored as distortion or deflection in the frame of the press and the dies.
These forces are suddenly released when the upper die breaks through the metal sheet resulting in objectionable shock, noise and vibrations. These loads increase correspondingly with the force employed in the stamping or shearing operation.
The shock, noise and vibrations adversely effect the press, surrounding equipment and persons located in the vicinity of the press. Further, these objections occur with each cycle of the press and increase with the force and size of the press.
Because of the noise and shock generated by presses in stamping and shearing operations, presses have been located in an area separate from other manufacturing operations, such as a separate building or a portion of a large building isolated from other manufacturing operations. This requires shipping, storage and additional handling of the stamped parts which increases their cost and results in the possibility of damage to the parts.
In order to alleviate or minimize the objectionable characteristics of stamping presses, attempts have been made to decrease the noise and vibration generated by a press. Such attempts incorporate shock dampening systems into the press which cushion the release of the stored forces via a hydraulic cylinder, restrictive fluid flow path, etc., in the hydraulic system of the press. Other systems control the speed of the press during its advance so as to decelerate the press when breakthrough of the workpiece occurs in order to minimize the impact of the upper die on the bed and frame of the press.
However, such attempts have met limited success in reducing the noise and vibration levels generated during a stamping or shearing press operation. Further, such attempts require additional components and controls which increases the cost of a press.
Thus, it would be desirable to provide a control system and method for a stamping or shearing press which reduces the noise and vibrations associated with the operation of stamping or shearing presses. It would also be desirable to provide a control apparatus and method for reducing noise and vibration levels in a stamping press which can be easily adapted to conventional press construction.